The present invention relates to a method for operating devices for transmitting high-bit-rate data on a subscriber line connecting a subscriber terminal device and a telephone exchange on which voice information and low-bit-rate data can also be transmitted. The method is implemented in the course of data transmission connections leading to a data communication network that bypass the central parts of the telephone exchange, whereby there can be a permanent connection between the devices at the subscriber side and at the network side and an access device of the data transmission network.
The present invention also relates to an arrangement having such devices for transmitting high-bit-rate data on a line.
Data transmission on subscriber lines that connect subscriber terminal devices to a telephone exchange, that serve primarily for transmitting voice signals and low-bit-rate data, and that are realized in the form of twisted pair copper wiring, plays a significant role because it would be very cost-intensive to lay separate subscriber lines to terminal devices which comprise other devices for generating and receiving data besides telephone devices, such as personal computers (PCs) and TV devices, and on the other hand, because of the available bandwidth, the existing copper cable network is poorly utilized by the telephone traffic alone. The history of what is known as copper access technology, that is, technology for digital transmission on copper cables, began with the now customary modems (modulator/demodulator). Modems which operate in the voice frequency range achieve transmission rates of up to 56 Kbit/s via existing telephone lines and have meanwhile almost reached the theoretically maximum transmission rates in the frequency region they use. Such modems transmit and receive in the same frequency region and were made possible only by great advances in digital signal processing, semiconductor technology and in the underlying algorithms.
These conventional modem connections do not meet the demand for a capability to transmit large data volumes such as are involved in connection with the aforementioned terminal devices, and furthermore, they do not provide a uniform transmission of voice and data via the subscriber line.
Some assistance is found in what is known as xDSL technology, whereby DSL stands for Digital Subscriber Line. In this technology, the copper line is divided into three different channels by inserting xDSL modems. One of these channels is still available for conventional telephone service, that is, for voice transmission (POTS: Plain Old Telephone Service). A second channel is made available for connecting the user to the service provider, and a third channel serves to transmit data from the service provider back to the customer. What are known as POTS splitters are typically used on the subscriber side and on the network side of the subscriber line in order to separate the voice channel from the data channels.
What is known as ADSL technology (Asymmetric Digital Subscriber Line) is a popular representative of xDSL technology, this designating a technology that allows the transmission of a high-bit-rate bit stream from a central office to the subscriber and the transmission of a low-rate stream that runs from the subscriber to the central office. Because of this asymmetric transmission technology with respect to bit rate, an ADSL system is suited to such services as video on demand. But ADSL is also particularly suitable for Internet applications, where the bit stream from the central office to the subscriber (downstream) is likewise typically of a significantly higher rate than the upstream bit stream, which primarily serves for transmitting control information relating to the selecting and requesting of data.
In contemporary ADSL technology, the transmission rate of the upstream channel typically varies between 16 Kbit/s and 640 Kbit/s, and the transmission rate of the downstream channel typically varies between 2,048 Mbit/s and 9.6 Mbit/s (depending, for example, on the type and length of cable).
Such high-bit-rate data transmissions are no longer handled completely via the telephone network, as is the case in the conventional modem connections described above; rather, they are branched onto a data transmission network so as to avoid the central parts of the telephone exchange. To this end, permanent connections are set up between the corresponding data transmission means at the subscriber side and at the network side and an access device to the data network. This means that the devices that terminate the extension line are in permanent operation even outside the context of data transmissions, so that excess operating current is made available, leading to unnecessary heat. This is a significant disadvantage, since there are a number of such devices in the service area of telephone exchanges that are unified in part into one assembly that combines the connection of several subscriber lines.